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Old 04-28-2010, 10:01 AM   #1
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Thermal Motor Breakers - 2 pole, with 3rd pin?


My first post here - be kind

I'm rewiring a 12VDC boat system that was hacked together by several previous owners from bits off everything from tractors to medical equipment. I have come across a thermal motor breaker, 2 pole, but with a much smaller 3rd pin. Its a TI Klixon CDLA-80 (80Amps) - no longer made.

The starter motor solenoid and the fuel pump connect to the positive rail via this mysterious third pin on the motor breaker. The breaker appears to protect the house wiring loom and house battery, but one side is connected to the starter battery via a battery isolator.

The pin is polarized too - reads short circuit wired -ve pole and +ve pin; reads open circuit wired +ve pole and -ve pin. So at the moment, it essentially disconnects the starter circuitry (far as I can tell).

So here's the question: I'm familiar with the purpose of motor breakers, but I don't understand what wiring the solenoid and fuel pump through this center pin is meant to achieve - I can make a few semi-educated guesses, but does anyone know for sure? How is that center pin supposed to function on a thermal motor breaker - reset, disconnect, override?
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Old 04-28-2010, 01:32 PM   #2
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sounds like it could be a switch . That wire(switch) will become live when needed on the motor. Like a disconnect for the motor, but you cant tell when the wire goes live or why without a ladder wiring diagram.

Thats what i think it could be.
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Old 04-28-2010, 02:04 PM   #3
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humberguy thoughtfully wrote:

Quote:
Originally Posted by humberguy View Post
sounds like it could be a switch . That wire(switch) will become live when needed on the motor. Like a disconnect for the motor, but you cant tell when the wire goes live or why without a ladder wiring diagram.

Thats what i think it could be.
No diagrams unfortunately - I can't even find a datasheet for the unit. I'm making diagrams as I go.

But you might be right about it being a switch - when I connect that wire to the unprotected positive rail, instead of the pin and leave the starter motor winding leads disconnected, the solenoid blows a fuse connected inline on that wire. So I'm thinking that the pin might be there to somehow protect the fuse (shared by momentary solenoid & continuous fuel pump), by only closing when the starter motor itself has power.

Can anyone confirm seeing that sort of arrangement?
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Old 04-29-2010, 09:56 AM   #4
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Ok folks - pardon the noise, it looks like my notes were jumbled, and it was the component next to the thermal regulator that was wired up the way I mentioned. Consider this one closed.
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